Significant research has been conducted in an effort to find polymer blends which have a combination of both elastic and thermoplastic properties. These polymer blends have been given the generic designation of Thermoplastic Olefins (“TPO”). They exhibit some of the properties of a cured elastomer as well as the reprocessability of thermoplastic resins. The elastomeric characteristics may be enhanced if one component of the blend is a vulcanizable elastomer which is wholly or partially crosslinked.
The earliest work in the curing of TPO compositions was by Gessler and Haslett in U.S. Pat. No. 3,037,954. That patent teaches the concept of “dynamic curing” wherein a vulcanizable elastomer is dispersed into a resinous thermoplastic polymer and the elastomer cured while continuously mixing and shearing the polymer blend. The result is a micro-gel dispersion of cured rubber in an uncured matrix of resinous thermoplastic polymer. Gessler's U.S. Pat. No. 3,037,954 discloses compositions comprising polypropylene and a rubber wherein the rubber may be butyl rubber, chlorinated butyl rubber, polybutadiene, polychloroprene and polyisobutylene. Compositions of 50 to 95 parts polypropylene and 5 to 50 parts of rubber are disclosed.
Dynamically vulcanized thermoplastic compositions comprising a polyamide and various types of elastomers are known. See, for example, U.S. Pat. No. 4,173,556; U.S. Pat. No. 4,197,379; U.S. Pat. No. 4,207,404; U.S. Pat. No. 4,297,453; U.S. Pat. No. 4,338,413; U.S. Pat. No. 4,348,502; U.S. Pat. No. 4,419,499, and U.S. Pat. No. 6,028,147. Specifically, U.S. Pat. No. 6,028,147 to Ogawa et al. discloses a triblock polymer including methylstyrene and p-(chloromethyl)styrene. Also, EP 0 542 875 to Dharmarajan et al discloses a polymer having halo para-methylstyrene derived unit within the polymer. None of these disclosures discloses a polymer having both meta and para-halogenated methylstyrenes and having improved durability and lower air permeability.